In this study, the effects of rosiglitazone on renal matrix metalloproteinase-9 (MMP-9) expression and its possible renoprotective mechanisms were investigated in streptozotocin-induced diabetic rats. We examined the urinary excretion rates of albumin (ALB), retinal-binding protein (RBP) and MMP-9 in control healthy rats (group C, n = 8), untreated diabetic rats (group D, n = 8) and diabetic rats treated with rosiglitazone (5 mg/kg/day) (group R, n = 8) at eighth week. The renal tissue of diabetic rats was obtained for observing renal pathological changes by electron microscope and examining the expression of renal MMP-9 mRNA by RT-PCR. Our results showed that urinary excretion rates of MMP-9. ALB and RBP were significantly increased concurrently with the expression of renal MMP-9 mRNA in group D compared with those of group C. Rosiglitazone significantly reduced urinary excretion rates of ALB, RBP and MMP-9 as well as the expression of renal MMP-9 mRNA. In addition, urinary excretion rate of MMP-9 showed positive relationship with urinary excretion rates of ALB and RBP. In conclusion, rosiglitazone definitely protects diabetic rats against renal injury, which may be partly associated with decreasing expression of renal MMP-9 mRNA and urinary MMP-9 production. © 2009 Blackwell Publishing Ltd.